| Isthminia | |
|---|---|
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Infraorder: | Cetacea |
| Family: | Iniidae |
| Genus: | † Isthminia Pyenson et al., 2015 |
| Species: | †I. panamensis |
| Binomial name | |
| †Isthminia panamensis Pyenson et al., 2015 | |
Isthminia is an extinct genus of river dolphin-like cetacean from the Late Miocene epoch (Hemphillian in the NALMA classification) that lived in Panama. The type species is I. panamensis. [1] [2]
Fossils of Isthminia were found in the Chagres Formation in Panama. On the basis of the fossil material, including a partial skull, the length of this kind is estimated to be about 285 centimetres (9.35 ft). Isthminia probably had a predominantly marine lifestyle. [1]
River dolphins are a polyphyletic group of fully aquatic mammals that reside exclusively in freshwater or brackish water. They are an informal grouping of dolphins, which itself is a paraphyletic group within the infraorder Cetacea. Extant river dolphins are placed in two superfamilies, Platanistoidea and Inioidea. They comprise the extant families Platanistidae, Iniidae and Pontoporiidae. There are five extant species of river dolphins. River dolphins, alongside other cetaceans, belong to the clade Artiodactyla, with even-toed ungulates, and their closest living relatives the hippopotamuses, from which they diverged about 40 million years ago. Specific types of Dolphins can be pink.
Iniidae is a family of river dolphins containing one living genus, Inia, and four extinct genera. The extant genus inhabits the river basins of South America, but the family formerly had a wider presence across the Atlantic Ocean.
Eobalaenoptera is an extinct genus of baleen whale belonging to Balaenopteroidea.
The evolution of cetaceans is thought to have begun in the Indian subcontinent from even-toed ungulates 50 million years ago (mya) and to have proceeded over a period of at least 15 million years. Cetaceans are fully aquatic marine mammals belonging to the order Artiodactyla and branched off from other artiodactyls around 50 mya. Cetaceans are thought to have evolved during the Eocene or earlier and to share a relatively recent closest common ancestor with hippopotami. Being mammals, they surface to breathe air; they have 5 finger bones (even-toed) in their fins; they nurse their young; and, despite their fully aquatic life style, they retain many skeletal features from their terrestrial ancestors. Research conducted in the late 1970s in Pakistan revealed several stages in the transition of cetaceans from land to sea.
Pakicetus is an extinct genus of amphibious cetacean of the family Pakicetidae, which was endemic to Pakistan during the Eocene, about 50 million years ago. It was a wolf-like animal, about 1 metre to 2 metres long, and lived in and around water where it ate fish and small animals. The vast majority of paleontologists regard it as the most basal whale, representing a transitional stage between land mammals and whales. It belongs to the even-toed ungulates with the closest living non-cetacean relative being the hippopotamus.
Squalodon is an extinct genus of whales of the Oligocene and Miocene epochs, belonging to the family Squalodontidae. Named by Jean-Pierre Sylvestre de Grateloup in 1840, it was originally believed to be an iguanodontid dinosaur but has since been reclassified. The name Squalodon comes from Squalus, a genus of shark. As a result, its name means "shark tooth". Its closest modern relative is the South Asian river dolphin.
Prosqualodon is an extinct genus of Early to Middle Miocene cetacean from Argentina, Australia, New Zealand and Venezuela.
Eurhinodelphis is an extinct genus of Miocene cetacean. Its fossils have been found in Belgium, France, and Maryland.
Kentriodon is an extinct genus of toothed whale related to modern-day dolphins. Fossils have been found in North America, Europe and Japan. Several species have been described so far.
Australodelphis mirus is an extinct Pliocene dolphin. A. mirus is known from fossils found in the Sørsdal Formation, Mule Peninsula, Vestfold Hills, East Antarctica. The genus has been described as an example of convergent evolution with beaked whales.
Kentriodontidae is an extinct family of odontocete whales related to modern dolphins. The Kentriodontidae lived from the Oligocene to the Pliocene before going extinct.
The Kokoamu Greensand is a geological formation found in New Zealand. It is a fossil-bearing, late Oligocene, greensand rock unit of the eastern South Island, especially the Waitaki District of North Otago and the southern Canterbury region. The formation was named by geologist Maxwell Gage in the 1950s. In North Otago it underlies the thicker and harder Otekaike Limestone. The formation gets its green colour from the mineral glauconite which forms slowly on the ocean floor.
Piscobalaena is an extinct genus of cetaceans, which lived from the Middle to Late Miocene epochs in Peru and Florida. Its fossils have been found in the Pisco Formation of Peru and the Bone Valley Formation of Florida. At least some individuals of this diminutive whale were preyed on by the shark C. megalodon.
The Chagres Formation (Tc) is a geologic formation in the Colón Province of central Panama. The sandstones and siltstones were deposited in a shallow marine environment and preserve fossils dating back to the Middle to Late Miocene period.
Huaridelphis is an extinct genus of river dolphins from the Early Miocene. The type species is H. raimondii, found in the Chilcatay Formation of the Pisco Basin.
Notocetus is an extinct genus of river dolphin belonging to Squalodelphinidae. Known specimens have been found in Early Miocene marine deposits from Argentina, Italy and Peru.
Arktocara is an extinct genus of river dolphin from the Oligocene epoch of Alaska, containing one species, A. yakataga. Having been discovered in 25-million-year-old strata near the 60th parallel north, it is perhaps the oldest known crown toothed whale and the northmost river dolphin discovered. It was a member of the now-extinct family Allodelphinidae, along with the genera Allodelphis, Goedertius, Ninjadelphis, and Zarhinocetus. It measured approximately 2.26 or 2.28 meters, comparable to its closest living relative, the South Asian river dolphin, which measures 2.4 meters (7.9 ft). However, the animal probably had an elongated beak and neck, so it may have been longer. The animal is known only from a partially preserved skull. Its ecology may have been similar to the modern day Dall's porpoise, and it may have competed with contemporaneous delphinoids. Its remains were found in the Poul Creek Formation, which has also yielded several mollusk species.
Brachydelphis is a genus of pontoporiid known from the Late Miocene Pisco Formation of Peru and the Bahía Inglesa Formation of Chile.
Brujadelphis is an extinct genus of river dolphin-like cetaceans of uncertain family placement from the Late Miocene epoch (Serravallian) of present-day Peru. The type species is Brujadelphis ankylorostris, recovered from the Pisco Formation.
Urkudelphis is an extinct genus of cetacean. The type species, Urkudelphis chawpipacha, was described in 2017 based on fossils found in the Dos Bocas Formation of Ecuador. It was a type of river dolphin.
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